Microelectrical mechanical systems (MEMS) are electro-mechanical structures typically sized on a millimeter scale or smaller. These structures are used in a wide variety of applications including for example, sensing, electrical and optical switching, and micron scale (or smaller) machinery, such as robotics and motors. Because of their small size, MEMS devices may be fabricated utilizing semiconductor production methods and other microfabrication techniques such as thin film processing and photolithography. Once fabricated, the MEMS structures are assembled to form MEMS devices. The fabrication and assembly of MEMS devices is typically called xe2x80x9cmicromachiningxe2x80x9d.
For optical switching, structures can be built which have a mirrored surface for reflecting a light beam from a sending input optical fiber to a separate receiving output fiber. By constructing a mirrored surface onto a movable structure, the mirror can be moved into, or out of, the path of a beam of light. With more than one switch aligned in the beam path, the beam can be directed to one of several receiving fibers. These types of structures are generally known as xe2x80x9coptomechanical switchesxe2x80x9d.
With optomechanical switches a common technique for moving mirrors and other structures is to employ one or more micromachined hinges. These hinges allow one structure to be rotated relative to another. With the use of a electrode, or other actuator, the movable structure attached to the hinge can be moved between two or more positions. For a structure with a movable mirror, the mirror is typically mounted out on an actuator arm which is hinged at its base. The mirror may use latches to fix it into a desired position.
With the actuator arm rotating about the hinge, the mirror can be moved into and out of a beam of light. As such, the hinge, by allowing the mirror to move between defined positions, enables the light beam to be switched between receiving devices such as various optical fibers, other mirrors, sensors and the like.
Another use for micromachined hinges is to facilitate the fabrication of MEMS structures. Hinges allow components built in common planes to one another, to be rotated to positions where the components are angled to one another. That is, by employing hinges, various non-planar structures can be created. The hinges also act to keep the base of the component in generally a fixed location while the component is rotated during construction. This results in a simpler construction process. An example of a construction hinge is a mirror set at a fixed angle to the actuator arm it is attached to. During the fabrication of this type of mirror, the mirror, actuator arm and latch are all etched out of aligned planar thin film layers. The mirror and the actuator arm are attached by a hinge. After the etching is complete, the mirror can be raised by placing a probe under the mirror and rotating it about the hinge until the latch is engaged and the mirror is locked into an upright or vertical position. After fabrication the mirror will not rotate about the hinge, but the hinge will continue to maintain the base of the mirror in a generally fixed position relative to the actuator arm.
Hinges can also be constructed both to enable construction of a structure and to allow rotational movement of the structure. One example of such a hinge use is with an actuator arm having a backflap which limits upward movement. The hinge is initially employed to allow the actuator arm to be raised and locked to the backflap at an angle relative to the backflap. Thereafter, the hinge operates to allow the actuator arm/backflap structure to rotate about the hinge. This results in a device that not only can move the actuator arm up and down, but limits the upward displacement of the arm.
In most cases, proper operation of MEMS devices are highly dependent on the specific positioning of the device""s components. For example, with optomechanical switches, the positioning of the mirror must be within specific limits to allow the light beam to be properly switched. Improper mirror positioning can cause the reflected light beam to not sufficiently align with the receiving device (e.g. an output optical fiber), cause only a portion of the beam to contact the mirror, or even cause the beam to miss the mirror all together. Any of these events can easily result in the failure of the switch and effectively of the entire switching device (array of switches).
With hinges it is desirable to limit any non-hinge-aligned rotational movements as much as possible. That is, to keep the components of the device positioned correctly, translational movements of the device along and/or lateral to the hinge are sought to be minimized. The more the components can slide or slip about the hinge, the greater the potential for failure of the switch. Further, if the component can move both along and lateral to the hinge, then it will most probably be able to rotate in a direction not aligned with the hinge (e.g. in a yawing motion). Such rotational movements can also easily cause switch failure.
One type of prior hinge is shown in FIG. 1. This type of hinge is set forth in xe2x80x9cMicrofabricated hingesxe2x80x9d, by K. S. J. Pister, M. W. Judy, S. R. Burgett and R. S. Fearing, in Sensors and Actuators, Vol. 33, pp. 249-256, 1992, which is herein incorporated by reference in its entirety. Referring to FIG. 1, the switch 100 has an actuator arm 110 which rotates about a hinge 120. The hinge 120 includes a hinge axis 122 and a hinge opening 124, a clasp 126 having supports 128 and a bridge 130. In this hinge the axis 122 is position between the supports 128. When the actuator arm 110 is in its lowered position (as shown in FIG. 1), one support 128 extends up through the opening 124. Extending between each support 128 and over the axis 122 is the bridge 130. The supports 128 and bridge 130 define a duct 132 and enclose the axis 122. The axis 122 is free to rotate within the duct 132 as the actuator arm 110 is raised and lowered.
The hinge 120 has play in it which is partly a result of using a sacrificial layers to separate the elements during the fabrication process. The play is also a result of limits due to process resolution and design rules. The play is further necessary to provide enough space for the square shaped axis 122 to rotate within the duct 132.
Although undesired movements of the actuator arm 110 are limited to some extent by the hinge 120 structure, the amount of movement is typically still sufficient to allow misalignment of the actuator arm 110. That is, the play existing in the hinge 120 allows the actuator arm 110 to slide either, or both, along the axis 122 or laterally towards one of the supports 128. Also, with the axis 122 moving in the duct 132 the actuator arm 110 can pivot in a yawing manner. Any of these undesired movements can produce a failure of the switch 100 due to misalignment of the mirror (not shown) mounted on the actuator arm 110. Failure can also occur in such a switch as the contact between the axis 122 and the clasp 126 will cause premature wear and breakage.
Another hinge switch is shown in FIG. 2. With switch 200, the actuator arm 210 is attached by hinge 220. The hinge 220 includes an anchor 222 and couplings 224. Because the couplings 224 have a relatively thin and elongated structure (shaped in an extended arch), the couplings 224., are sufficiently deformable to allow the actuator to rotate about the hinge 220. The hinge 220 is etched from the same layer of material as the actuator arm 210 and the anchor 222 extends downward and connects to the surface 205 of the switch 200.
While the hinge 220 is simpler to construct than the hinge 120, it retains at least some of the unwanted play of the hinge 120. Specifically, in addition to allowing the actuator arm 210 to rotate, the couplings 224 also allow the actuator arm 210 to move in a lateral direction away from the anchor 222. That is, the couplings are flexible enough that the actuator arm 210 can be displaced outward from the hinge 220. In addition, the actuator arm 210 can move in other undesired directions including translationally along the length of the hinge 220 and can rotate about the hinge 220 in an yawing manner. As with the hinge 120, any of the possible undesired movements of the hinge 220 can result in failure of the switch 200.
Therefore, a need exists for a mircomachined hinge structure which eliminates or at least sufficiently minimizes all undesired movements about the hinge. Such a hinge structure must at the same time retain the ability of the hinge to allow the attached component to rotate freely in the desired direction. The hinge should further be capable of allowing repeated rotations of the attached component and/or to enable construction of the device by facilitating the rotation of one component relative to another and maintaining the position thereafter. The hinge should be capable of exerting a biasing force to urge the actuator arm to a desired position.
In at least one embodiment, the apparatus is a thin film structure having a first structure, a second structure, and a hinge coupled between the first and second structures. Where the hinge has a first flexible member aligned substantially along an axis. The hinge is arranged so that the second structure can rotate relative to the first structure substantially about the axis.
In other embodiments, the hinge can also include a second flexible member aligned substantially along the axis. The first and second flexible members being positioned on opposite side of the second structure.
In some embodiments the apparatus is a MEMS optical switch having a substrate surface, an actuator arm with a mirror, and a hinge mounted between the substrate surface and the actuator arm. The hinge functions to allow the actuator arm to rotate relative to the substrate surface. The hinge has a first anchor, a second anchor, a first flexible member, a second flexible member, and a central section. The central section is mounted to the actuator arm. The first and second flexible members are connected to opposing sides of the central section substantially along an axis. The first anchor is mounted between the first flexible member and the substrate surface. Similarly, the second anchor is mounted between the second flexible member and the substrate surface.
In at least one embodiment, the method includes providing a first structure, forming over the first structure a sacrificial layer with a first via to the first structure, forming a hinge with a first anchor attached through the first via to the first structure and a first flexible member attached to the anchor, forming a deflectable structure attached to the hinge at the first flexible member, and removing the sacrificial layer so the deflectable structure may rotate about the hinge.